CHEMICAL ELEMENT BALANCE METHOD APPLIED TO DICHOTOMOUS SAMPLER DATA

Between 1970 and 1976, substantial progress was made in reducing the amount of suspended particulate matter in many parts of the United States. During 1970, for example, 60% of the population in the New York Air Quality Control Region was exposed to total suspended particulate concentrations that exceeded the annual National Ambient Air Quality Standard of 75 wg m-3, By 1976, particulate concentrations were sufficiently reduced so that the entire region met the standard.’ Nonetheless, many regions of the United States are still not meeting the National Air Quality Standard.’ To make further progress in the control of particulate matter, it would be valuable to know its composition and major sources. Miller et a / . have developed a chemical element balance method for resolving the chemical composition of airborne particles into components from several types of emission sources.’ Data on the concentrations of several elements were used to determine the abundance of sea salt, soil, automobile emissions, and fuel-oil fly ash in total suspended particulate matter at Pasadena, California.2 Later, Friedlander applied the method for Pasadena, including additional components for Portland cement and rubber tire dust.‘ Winchester and Nifong4 and Gatz’ used element balance methods to estimate source components for the Chicago area. Recently, Kowalczyk et al. resolved aerosol in the Washington, D.C. area into the following six components: soil, marine, coal, oil, refuse incineration, and motor vehicle emissions.6 By adding sulfate and nitrate to their predicted six components, Kowalczyk et al. were able to account for about 80% of the total suspended particulate mass! In the present work, the chemical element balance method is applied to aerosols collected in ten dichotomous samplers in the vicinity of St. Louis, Missouri, as part of the Regional Air Pollution Study (RAPS):’ and in the Great Smoky Mountain National Park at Elkmont, Tennessee. The dichotomous sampler collected particles in two size ranges9 corresponding to the two major modes of the bimodal distribution of aerosol mass reported by Whitby et al.” The fine fraction collected by the dichotomous sampler consists mostly of particles from combustion sources and secondary aerosol, and the coarse fraction consists mostly of mechanically generated aerosols. Dichotomous samplers’ in RAPS were operated in the St. Louis vicinity between May 1975 and March 1977 at locations shown in FIGURE 1. The present work is based upon RAPS data for July and August of 1976. For the study in the Smoky Mountains, samples were collected from September 20 to 26 of 1978.